Somehow there are two months missing from the date dropdown-field when creating or editing blog posts. It has worked before and I can't remember making any changes that could have affected this, other than changing the server PHP version to a higher one (7.2). The affected months have ä (a umlaut) in them. I even tried lowering the PHP version but it didn't help.
I attached a screenshot of the problem. Might anyone have first-hand knowledge or tips for me to solve this problem? I will be grateful for any help on this matter!